Sleep is something we generally associate with living person

Sleep is something we generally associate with living persons or animals.Of course,it is true that a lot of animal sleep,but zoologists are not certain that primitive forms of animal life,like worms ever really sleep.On the other hand,animals such as bears sleep for 4 or 5 months every year.
The amount of sleep human being need varies with people of different ages,habits and possible races.For example,doctors think that pre-school children need between 10 and 12 hours a night；school children between 9and 11 hours;and adults between 7and 9 hours.There are rare cases of old people who only sleep between 2 and 3 hours a day and continue to be active and healthy.The sleep requirements of different races also appear to be different.Japanese people ,for example,sleep fewer hours than Europeans.
It is known for certain if the activity of a man’s mind (besides dreaming) occurs when he is asleep.Howere ,it is certainly true that some people can wake up at a pre-determinded time.There are also stories about some maths professon who solve difficult problem during sleep,because their subconscious minds continue working on the problem.
Question:
1.What is the passage mainly about?
2.According to zoologists,primitive forms of animal life¬¬（ ）.
3.What does the writer try to show in the second paragraph?
4.What is ture about Eruopeans when talking about sleep?
5.When a man is asleep,what is subconscious mind probably doing?

1 Sleep is something we generally associate with living persons or animals
2 sleep or not
3 differenet age of people need different sleep time
4 they sleep more hours than Japanese people